Advanced semiconductor fabrication is employing increasing vertical circuit integration as designers continue to strive for circuit density maximization. Such typically includes multi-level metallization. Electrical interconnect techniques typically require electrical connection between metal layers or other conductive layers which are present at different elevations in the substrate. Such interconnecting is typically conducted, in part, by etching a contact opening through insulating material to the lower elevation metal layer or conductive region. Increased circuit density has resulted in narrower and deeper electrical contact openings between layers within the substrate. Adequate contact coverage within these deep and narrow contacts continues to challenge the designer in assuring adequate electrical connection between different elevation areas within the substrate.
As transistor active area dimensions approached one micron in diameter, conventional process parameters resulted in intolerable increased resistance between the active region or area and the conductive layer. The principal way of reducing such contact resistance is by formation of a metal silicide atop the active area prior to application of the conductive film for formation of the conductor runner. One common metal silicide material formed is TiSi.sub.x, where x is predominantly "2". The TiSi.sub.x material is typically provided by first applying a thin layer of titanium atop the wafer which contacts the active areas within the contact openings. Thereafter, the wafer is subjected to a high temperature anneal. This causes the titanium to react with the silicon of the active area, thus forming the TiSi.sub.x. Such a process is said to be self-aligning, as the TiSi.sub.x is only formed where the titanium metal contacts the silicon active regions. The applied titanium film everywhere else overlies an insulative, and substantially non-reactive, doped or undoped SiO.sub.2 layer.
Ultimately, an electrically conductive contact filling material such as tungsten or aluminum would be provided for making electrical connection to the contact. However, tungsten adheres poorly to TiSi.sub.x. Additionally, it is desirable to prevent intermixing of the contact filling material with the silicide and underlying silicon. Accordingly, an intervening layer is typically provided to prevent the diffusion of the silicon and silicide with the plug filling metal, and to effectively adhere the plug filling metal to the underlying substrate. Such material is, accordingly, also electrically conductive and commonly referred to as a "barrier layer" due to the anti-diffusion properties.